Are we alone?

Does life exist anywhere in the Universe apart from on Earth? Scientists have been searching for life elsewhere in the Universe for more than 100 years. What are the chances of success?

As the likehood of intelligent life existing elsewhere in the solar system disappeared, people began to think about the possibility of life existing farther away in the universe. If the canals that Schiaparelli and Lowell thought they had seen on Mars did not actually exist and neither did the beings who were thought to have engineered them, then perhaps we just had to look farther afield to find intelligent beings. There was no point in looking for life on the remaining solar system planets, because, apart from Earth and possibly Mars, all the others were simply too hostile to support life as we know it. But perhaps one of the points of light in the night sky could be a sun-like star with a collection of planets around it. And perhaps being similar to ourselves had evolved on at least one of them.

Crossing oceans of space
How were scientists to make contact with any distant civilizations that do exist? The distances to the stars are measured in light years. It is not (yet) possible for us to travel to the stars and look for other beings ourselves because the spacecraft we have now are too slow. When the Apollo spacecraft broke free from the earth's gravity and headed for the moon, it was traveling at about 40,000 kph. That is the fastest that people have traveled so far. At this speed, it would take a spacecraft more than 150,000 years to travel the 43 million kilometres between us and the closest star, Proxima Centauri. Unmanned probes that space scientist knew would fly out of the solar system towards the stars one day have been given messages to take to any beings who discover them thousands or perhaps millions of years from now. We have sent for spacecraft to the stars-Pioneers 10 and 11, and Voyagers 1 and 2.

The most practical way to seek out extraterrestrial life is to send something that can travel much faster than spacecraft radio waves. Radio waves travel at the speed of light-300,000 kilometres per second. They can reach the nearest star in only 4.3 years. There are two ways of using radio to establish contact with beings from another civilization. We can search for radio signals that they might have transmitted or we ourselves can transmit our own radio messages out into space, in the hope that someone might receive them and answer.

Radio Search
On October 12th 1992, the 500th anniversary of Columbus's discovery of the New World, NASA embarked on its latest project to discover new worlds in space. The agency is spending US $100 million over 10 years on the most advanced search yet for life elsewhere in the universe. The main dish at the Araceibo radio observatory on the island of Puerto Rico and other radio telescopes that form NASA's Deep Space Network (DSN) will be used to collect more radio signals from space than all other radio telescopes added together. About 800 sun-like stars will be monitored at a billion different radio frequencies. The whole sky will also be swept by the telescopes, but fewer frequencies will be monitored.

Spot facts:

In the 1960s a team of Cambridge astronomers who were not working on SETI (the Search for Extra-Terrestrial Intelligence) at all thought they might have detected radio messages from intelligent beings. Their radio telescope picked up radio signals from a star that seemed to be ticking with an unnatural regular rhythm. One of the possibility was that this was a radio message sent by intelligent beings on a planet orbiting the star. In fact, it was the star itself that was ticking. The team had detected the first pulsating star, or a pulsar - a neutron star, the remains of a supernova.

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